Enteral feeding is a form of hyperalimentation and metabolic support in which nutrient formulas or medicaments are delivered directly to the gastrointestinal tract, either the stomach or the duodenum. Nutrient administration is accomplished through use of an enteral feeding system or device. Certain enteral feeding devices include pumps which deliver feeding fluid to the patient. Other enteral feeding devices rely upon gravity to move the feeding fluid from a container (suspended above patient level) to the patient.
During enteral feeding, excessive gastric pressure may result from the accumulation of gas or liquid resulting from stomach contractions, movement of the patient's abdomen, crying or through normal formation of gas. From time to time, the body relieves such excess gastric pressure by expelling gas or liquid or reflux fluid. The term, “reflux fluid” as used herein includes any gas, any liquid, any partially solid and liquid substance or any material which the body can expel.
Typically the expulsion of reflux fluid occurs during a burping response in which reflux fluid is expelled upward from the stomach through the esophagus and is expressed out of the mouth, where the enteral feeding tube is orally intubated or through the nasal passages, where naso-pharyngeal intubation has been utilized. When the patient expels reflux fluid, the reflux fluid often flows out of the patient's mouth or the nose. The enteral feeding device is not adapted to receive the back flow of reflux fluid. Specifically, the feeding fluid pressure in the enteral feeding device prevents reflux fluid from flowing from the patient into the patient feeding tube.
Though gastric reflux pressure created by even limited episodes of stomach movement or crying may exceed several feet of water, such reflux pressure can be inadequate to overcome the greater forward fluid pressure present within the patient feeding tube. As a result, expelled reflux fluid can be trapped or accumulate in or around the nasal, oral, or pharyngeal passages, which often can lead to complications. This accumulation of reflux fluid is undesirable because the patient loses feeding fluid, and moreover, it is possible for the patient to inhale the reflux fluid into the lungs with possible risk of aspiration pneumonia, bacterial infection in the pharynx or esophagus, or other ailments. The problem of gastric reflux pressure and reflux fluid is most acute in neonates, infants and small children in which gastric pressure may rapidly accumulate through periodic episodes of crying and because such patients have yet to develop control over the burping response as a means of gastric pressure relief. However, it is not unusual for adult patients undergoing enteral feeding to experience occasional difficulties with gastric reflux pressure relief.
Over the years, enteral tubes for providing food and medication to a patient have been used in medical settings for many years. For examples of enteral feeding devices are described in U.S. Pat. Nos. 4,666,433, 4,701,163, 4,798,592, or 4,685,901. The measurement of esophageal and gastric pressures with balloon-tipped catheters also has been employed with great success over the past half century to delineate the physiology of the respiratory system. Gastro-esophageal reflux (GER) and bronchoaspiration of gastric content are risk factors linked with ventilator-associated pneumonia. Gastroesophageal reflux (GER) occurs in critically ill patients even in the absence of nasogastric (NG) tubes and enteral feedings; up to 30% of patients who are kept in the supine position are estimated to have GER. At least two studies have shown a reduction of GER when critically ill patients are kept in the semirecumbent position. The upper gastrointestinal tract of a critically ill patient receiving enteral feedings is additionally challenged by (1) gastrointestinal intubation, (2) rate of feeding, and (3) type of enteral formula.
The lower esophageal sphincter (LES) has been recognized for more than three decades as the primary physiologic factor preventing GER. A number of studies in adults and children with or without reflux disease have examined the relationship of LES pressure to occurrence and time of reflux, using concurrent measurements of esophageal motility and pH. One consistent finding has been that under resting conditions, LES pressure has to be absent for reflux to occur. The NG tube may predispose a patient to reflux by interfering with LES function, as well as prolonging esophageal contact time with refluxed gastric contents.
The majority of enteral feeding tubes remain in the stomach. Regurgitation occurs even in patients with well-placed NG tubes and less frequently in patients with nasoduodenal (ND) or nasojejunal (NJ) tubes. Several studies have shown that NG tubes may increase the prevalence of GER in supine patients from 15% to 80% of cases. Placement of an NG tube may be associated with profound esophagitis within a 24-36-hour period, although it is more commonly observed after a week or more of intubation.
Fluids that commonly accumulate in the gastrointestinal tract of a tube-fed patient include the tube-feeding formula, swallowed saliva (>0.8 L/day), gastric secretion (1.5 L/day), and regurgitated small bowel secretion (2.7-3.7 L/day) into the stomach. When gastrointestinal motility is normal, secretions and ingested fluids are propelled forward and absorbed with little difficulty. Significant gastrointestinal dysmotility, ranging from moderate delay in gastric emptying to marked gastric paresis, has been described in patients with a variety of clinical conditions such as burns, sepsis, trauma, surgery, and shock.